1. Field of the Invention
The present invention relates to a mobile communication system, a mobile communication method, a mobile station, and an exchange.
2. Description of the Related Art
In conventional mobile communication systems, for example, all mobile stations of passengers on a train start transmission of a location registration request at the same time when the train crosses over from one location registration area to another location registration area, which causes a problem that overloads for processing are imposed on radio capacity and an exchange.
In addition, there is also another problem that when a large amount of calling processing is performed at the same time for a specific event (for example, application for a TV program or the like), the transmission of calling requests for performing the calling processing causes overloads for processing on a radio capacity and an exchange.
To solve these problems, current 3GPP specifications define “Domain Specific Access Control (hereinafter referred to as DSAC)”. In accordance with the DSAC, a mobile communication system is configured to separately restrict processing in a circuit switch and processing in a packet switch if congestion is caused in a network.
Note that a mobile communication system to which the DSAC is not applied is configured to restrict (prohibit) all the processing in a circuit switch and a packet switch when congestion is caused in a circuit switched network or a packet switched network. Accordingly, a mobile station cannot perform calling/call-receiving processing and location registration processing through either the circuit switch or the packet switch.
In addition, a mobile communication system to which the DSAC is applied has a configuration in which, when congestion is caused in a circuit switched network or a packet switched network, all the processing is prohibited in a domain having the congestion caused, that is, in an exchange (a circuit switch or a packet switch) in the network having the congestion caused. Thus, the mobile station cannot perform calling/call-receiving processing and location registration processing through the exchange (the circuit switching exchange or the packet switching exchange) in the network having the congestion caused.
Referring to FIGS. 1 to 3, the description will be given of an operation to restrict processing performed in each exchange in a mobile communication system to which a conventional DSAC is applied.
As shown in FIGS. 1 to 3, at step S1000, a circuit switching exchange MSC or a packet switching exchange SGSN detects congestion caused in a circuit switched network or a packet switched network.
At step S1001, the exchange detecting the congestion (the circuit switching exchange MSC or the packet switching exchange SGSN) transmits, to the radio network controller RNC, “a CS restriction indication” or “a PS restriction indication” for instructing to restrict all the processing in the circuit switching exchange MSC or the packet switching exchange SGSN.
At step S1002, the radio network controller RNC creates broadcast information including the received CS restriction indication or the PS restriction indication. At step S1003, the radio network controller RNC transmits the created broadcast information through a radio base station BTS to a location registration area belonging to the radio network controller RNC.
As a result, the mobile station cannot perform the calling/call-receiving processing and the location registration processing through the exchange (the circuit switching exchange or the packet switching exchange) in the network in which congestion is caused.
[Non-patent Document 1] 3GPP TS.24.008 V6.1.2.0 (6.c.0), issued in March 2006
[Non-patent Document 2] 3GPP TS.25.331 V6.5.0, issued in March 2005
In general, a main factor of congestion in a network is specific processing like location registration processing, calling processing, and the like. Thus, in many cases, it is sufficient to restrict only some of such processing in an exchange, that is, it is not necessary to restrict all the processing in the exchange.
However, a mobile communication system to which the conventional aforementioned DSAC is applied is configured to restrict all the processing in a circuit switch or a packet switch for all mobile stations that belong to a specific location registration area. For this reason, there is a problem that such unnecessarily-prohibitive restrict affects call-receiving processing of a mobile station in the area, which processing essentially should not be restricted, or location registration processing by a mobile station which moves to the specific location registration area.